#define _CRT_SECURE_NO_WARNINGS 1
class Solution {
public:
    int climbStairs(int n)
    {
        int ret = 2, p = 0, q = 1;
        for (int i = 1; i <= n; i++)
        {
            ret = p + q;
            p = q;
            q = ret;
        }
        return ret;
    }
};